Variation of water quality in a river in the Southeast region of Brazil in the long term (1978-2018) according to the IQA and VAT indices

Abstract

The objective of this work was to analyze the long-term trend of water quality behavior of the Jacaré-Guaçu River, at the CETESB monitoring point further downstream of this river, near its mouth. Jacaré-Guaçu is an important river in the central region of the State of São Paulo, receiving through its tributaries discharges of the cities of São Carlos and Araraquara, among others. The analysis was based on the results of the IQA and IVA quality indices contained in CETESB monitoring reports, in the periods 1978-2018, for the IQA, and from 2002-2018, for the IVA, determining the annual averages and the three-year moving averages of these indices. The results show for the IQA a downward trend (worsening) in the period 1981-2003 and ascending (improvement) from 2004-2018, and for the entire period studied the general trend is downward (worsening). For IVA there is a downward trend (improvement) from 2002-2013, upward (worsening) in 2014-2018 and, overall, from 2002-2018, an improvement. The annual and moving averages of the indices for the rainy and dry periods were also determined and the resulting trend was that both IQA and IVA show better results in the dry period. It was concluded that these indexes and respective moving averages were adequate to verify the behavior of water quality at the studied point, which had a better trend in the dry period, probably due to the transport of diffuse polluting loads to the river by the surface runoff of rainwater.